9509211 Basolo One model for the evolution of female mating preferences, the preexisting bias model, suggests that a bias favoring a trait can arise prior to the trait itself. This model has been suggested to influence the evolution of a female preference favoring a sword and sword evolution in the genus of fish, Xiphophorus. Swords are multi-colored extensions of a specific set of caudal rays at the base of the caudal fin found in a number of species of Xiphophorus. Previous work suggests that swordlessness is the ancestral state, as all outgroups to this genus lack a structure homologous to the sword. In the three species of Xiphophorus that have been tested, one species that possesses a sword and two other species lacking swords, females have been shown to prefer conspecific males with swords. In addition, in the sister genus, Priapella, females have also been shown to have a preference favoring a sword. Using parsimony, it appears that while swords arose within the genus Xiphophorus, a preference favoring the sword arose prior to the divergence of Priapella and Xiphophorus. These results then suggest that the preference arose prior to appearance of the sword and can be explained by the preexisting bias model for the evolution of female preferences for male traits. This proposal is to compare the strength of a female preference favoring a sword across species. While two of the species share the preference, one exhibits the ancestral condition for the trait, i.e. lack of a sword, and the other exhibits the derived condition, i.e. presence of a sword. Presence of the preference has not previously been tested in the third species to be examined and it lacks a sword. ***
